It is conventional to store spent nuclear fuel assemblies in racks on the floor of a storage pool. It would, however, be desirable to increase the storage capacity of a rack. It has been proposed to achieve this by disassembling the rods from the fuel assembly in a remote area of the pool. This may be accomplished, for example, by cutting the top end fitting from the assembly and pulling out the fuel rods. The skeleton of the fuel assembly can then be compacted and disposed of in a commercial burial ground. The fuel rods would be loaded into a canister having approximately the same external dimensions as the fuel assembly. A cap would be sealed on the end of the canister and the canister lowered into a cell in the storage rack. As the rods can be close packed in the canister, it should be possible to achieve a compaction ratio of 1.5:1 to 2:1. In other words, the fuel rods of as many as two fuel assemblies may be stored in one cell of a fuel storage rack.
One problem which arises in implementing this concept is a result of the requirement that the rack must be designed to withstand a seismic event. A fuel assembly may weigh on the order of 1,500 pounds and there may typically be one-half inch clearance between the outside of the fuel assembly and the inner wall of a cell. For example, the cell may be 9 inches square and the fuel assembly may be 81/2 inches square. In order to withstand an earthquake, the designer must employ an impact factor. This might be, for example, a factor of 2:1. Thus, for a 1,500 pound fuel assembly, the cell and rack would have to be designed to withstand a 3,000 pound load.
In going from fuel assembly storage to loose rod storage at 2:1 consolidation, 3,000 pounds of fuel rods may be placed in each cell. If impact is considered, the cells must be designed for a 6,000 pound load. However, if the impact factor can be disregarded and eliminated, redesign of the cells may be avoided.
It would also be desirable to reduce the horizontal seismic loads imposed by a rack on the pool floor.